This application relates to an Oldham coupling for a scroll compressor. In particular, this application relates to a scroll compressor used in a refrigeration system, although the invention is not limited in use to refrigeration systems.
In typical scroll compressors, a first, stationary, scroll member has a base and a generally spiral wrap extending from its base. A second, orbiting, scroll member has a base and a generally spiral wrap extending from its base. The second scroll member is driven to orbit by a rotating shaft. An eccentric pin on the shaft extends into a slider block which is received within a boss on a rear face of the second scroll member. A special coupling, known as an Oldham coupling, allows the second scroll member to orbit relative to the first scroll member when driven by the rotating shaft. As the second scroll member orbits relative to the first, compression chambers defined between the wraps of the first and second scroll member decrease in size to compress the refrigerant.
Typical Oldham couplings may demonstrate a fatigue failure in the web structure when one or more guides or keys become worn.
Fatigue failure of the Oldham Coupling across its web structure is a critical failure mode of the coupling. Quite often wear of one or more guides or keys precedes the failure. Poor lubrication conditions may promote wear and subsequent fatigue failure of the Oldham coupling, particularly during a low speed defrost often associated with a liquid refrigerant flood back. An Oldham coupling with worn keys reorients itself in a position that induces extra loads on the web leading, potentially, to its fracture. However, fracture of the web has been observed even with non-worn keys. Accordingly, the keys' wear was considered a major precursor of the failure in former attempts to resolve the issue of fracture in the web. Earlier attempts to eliminate failure of the coupling were concentrated on reducing wear of the keys by utilizing wear resistant coatings on the keys and reducing access of a liquid refrigerant to the area of keys/scroll interaction.